The present invention relates to a set of split bodies for forming a synthetic resin blower fan through a so-called hollow-article injection molding process, and more specifically to a set of split bodies for forming a synthetic resin blower fan including a plurality of radial airflow passages formed between a circular base and a doughnut-shaped cover portion having an air inlet opening, through the hollow-article injection molding process.
Heretofore, blowers for generating airflow have been used in various operating machines such as power blowers and sprayers. Each of the blowers includes a blower fan rotatably driven by any suitable drive unit such as an air-cooled two-cycle internal combustion engine. Regardless of the type of blowers, the blower fan has a similar structure which integrally includes a circular base, a doughnut-shaped cover portion having an air inlet opening at the center thereof, and a plurality of blades each extending radially between the circular base and the inner surface of the cover portion to define a plurality of radial airflow passages between the adjacent blades.
Typically, in the conventional blower fun, the inner surface of the cover portion is screwed or riveted integrally to a boss formed in each of the blades by partially increasing the thickness thereof.
The blast performance of the blower fan has a significant dependence on the configuration of the airflow passages defined by the blades. In the conventional method, it is required to form the bosses in the blades, which imposes restrictions in design. The subsequently required operation such as screwing causes increased labor and time in manufacturing processes.
On the other hand, there has been known a hollow-article injection molding process disclosed, for example, in xe2x80x9cNikkei Mechanicalxe2x80x9d (Vol. 12, May/2000, pp 122-127), Japanese Patent Publication No. 2-38377, and Japanese Patent Laid-Open Publication No. 11-138584. The hollow-article injection molding process disclosed in these publications can be summarized as follows. Primarily, a pair of split bodies to be jointed together are molded separately by using a set of dies with molten synthetic resin. Secondary, the dies are moved without releasing the split bodies therefrom to butt the split bodies together, and molten synthetic resin is injected into a space formed in the periphery of the butted portion of the split bodies which are still at high temperature. Thus, the periphery of the butted portion of the split bodies are fused by the heat of the injected molten synthetic resin, and thereby the spilt bodied will be fusedly jointed together through the injected molten synthetic resin itself. The term xe2x80x9chollow-article injection molding processxe2x80x9d herein means the above method.
Generally, the hollow-article injection molding process includes two processes: a DSI (Die Slide Injection) molding process and a DRI (Die Rotating Injection) molding process. In the DSI molding process, After forming a pair of split bodies as primary molded components, a set of dies are opened while leaving the split bodies therein, and the respective dies are slid (linearly moved) to butt the split bodies together. Then, the split bodies are fusedly jointed together through a secondary injection molding. In the DRI molding process, a set of dies are rotated while leaving therein a pair of split bodies as primary molded components to butt the split bodies together, and molten synthetic resin is injected into a space formed between the butted surfaces of the split bodies to fusedly joint the split bodies together. The term xe2x80x9chollow-article injection molding processxe2x80x9d herein means the aforementioned method independently of the movement direction of the molting dies.
It is an object of the present invention to provide a set of split bodies for allowing an integral blower fan to be reliably formed without difficulty through the hollow-article injection molding process.
In order to achieve the above object, the present invention provides a set of split bodies for forming a synthetic-resin blower fan through a hollow-article injection molding process, wherein the blower fan includes a circular base, a doughnut-shaped cover portion having an air inlet opening at the center thereof, and a plurality of blades each extending radially between the circular base and the inner surface of the cover portion to define a plurality of radial airflow passages between the adjacent blades. The set of split bodies comprises a first split body including the circular base and a plurality of blade members serving as respective substantial parts of the blades, and a second split body defining the inner surface of the cover portion and having an outer surface on the opposite side of the first split body. The outer surface of the second split body is formed with a plurality of reservoirs each extending radially in alignment with the corresponding blade member of the first split body to define spaces to be filled with molten synthetic resin in a state where the first and second split bodies are assembled together. Further, each of the reservoirs having a bottom wall formed with a through hole adapted to allow an upper portion of the blade member to be inserted therethrough and tightly fitted therein so that the terminal end of the blade member is exposed into the corresponding reservoir in the assembled position.
The set of split bodies according to the present invention is formed and jointed in the following process. After appropriately preparing a set of dies for defining therebetween first and second cavities, the first and second split bodies are primarily molded by injecting molten synthetic resin into the first and second cavities, respectively.
After the primary injection molding, one of the dies is moved while leaving the first and second spilt bodies separately in the opposite dies. At this moment, the second split body is left in the second cavity for forming the upper surface thereof. Then, the dies are relatively moved to allow the blade members of the first split body and the corresponding through holes of the second split body to be opposedly aligned with one another, and then the respective upper portions of the blade members are inserted into the corresponding through holes. Thus, each of the through holes is closed by the upper portion of the blade member. In this position, the respective terminal ends of the blade members are exposed into the corresponding reservoirs.
The surface of the second cavity receiving the second split body therein may be configured to close the respective reservoirs on the opposite side of the through holes closed by the upper portions of the blade members so as to define a flow channel for allowing molten synthetic resin to flow therein. That is, in the present invention, the flow channel is defined by closing the reservoirs by use of the surface of the die.
One of the dies for leaving the second split body therein is appropriately provided with an injection port opened to the reservoirs or the flow channel to inject the molten synthetic resin therethrough, and a gas-vent hole opened to atmosphere.
In the above position, molten synthetic resin is injected from the injection port. The molten synthetic resin flows in the reservoirs or the flow channel to push out air in the channels to atmosphere through the gas-vent hole formed in the die. In each of the reservoirs, the molten synthetic resin contacts the inner wall of the reservoir and the terminal end of the blade member, and thereby the surfaces of the inner wall and the terminal end are appropriately fused by the heat of the molten synthetic resin. Gas caused by the fusion of the synthetic resin of the split bodies is also discharged from the gas-vent hole to atmosphere. When the revivers or the flow channel is fully filled with the injected molten synthetic resin, the injection operation is completed. Then, the finished blower fan is released from the dies. An operator can determined if the reservoirs are fully filled with the synthetic resin, only by visually checking the outer surface of the blower fan.
The set of split bodies according to the present invention allows the blower fan to be integrally formed through the injection molding process, which provides simplified manufacturing processes. In addition, the respective upper portions of the blade members are fusedly jointed to the second split body through the hollow-article injection molding process. This eliminates the need for providing the bosses used in fixing the doughnut-shaped cover portion (side plate) to effectively remove the restrictions in the design of the airflow passages. Thus, the structure of the blower fan can be flexibly designed in terms of its performance.
Further, the surface of the die is used to close the opened reservoirs and form the closed flow channel for receiving or guiding the injected molten synthetic resin. This eliminates the need for forming a wall for closing the flow channel, in the second split body having a restriction on its thickness, and provides increased volume of the flow channel. Thus, the injected molten synthetic resin can be sufficiently injected without its sharp temperature drop, and thereby the walls in the flow channel can be reliably fused as much as required to provide enhanced connection strength.
In a specific embodiment of the present invention, the upper portion of the blade member may be provided with a protrusion adapted to extend into the reservoir with a certain gap formed between the outer peripheral surface of the protrusion and the inner peripheral surface of the reservoir in the assembled position.
Further, the bottom wall may have a raised portion extending from the inner surface toward the blade member so as to allow to increase the depth of the reservoir to increase the height of the protrusion to be adapted into the reservoir in the assembled position.
In another embodiment of the present invention, the upper portion of the blade member may include a step portion around the lower end thereof. The step portion extends in the thickness direction of the blade member. Further, the step portion is adapted to contact a part of the inner surface of the second split body surrounding the through hole in the assembled position.